Electric mower hit metal rod, sounds bad when on now.

I have a 21' Greenworks Electric self propelled lawn mower. I was trying to clean up around a shed in the house I'm now living in and there was a metal rod stuck in the ground and shoved over side ways for some reason and I hit it with the lawn mower. It sounded terrible afterwards. I thought maybe the blade was bent, but it looks fine. There is a circular piece under the blade that seems to also be spinning with the blades and makes the blades sound very wobbly and weak when on. It sometimes sounds fine then very starts sounding terrible. I tried to attach a video of it but it only seems to allow pictures. Does anyone know what is going on or what this piece is? Is it replaceable? I spend 500 on this lawn mower and have no other way to keep around my home clean